Spring suspension system, in particular for a machine

ABSTRACT

1. Spring suspension system, in particular for a machine.  
     2. The invention relates to a spring suspension system, in particular for a machine such as a tractor or the like, with a spring suspension cylinder ( 10 ) to which varying load pressures (m) are applied, the piston ( 12 ) and rod ( 14 ) sides of which suspension cylinder may each be connected to a suspension reservoir ( 16, 18 ) by way of a locking device ( 20 ) which blocks the spring suspension and with an equalization device ( 28 ) which effects equalization of the pressure of the system to the currently prevailing load pressure (m) prior to activation of the spring suspension. Consequently, with the spring suspension system claimed for the invention pressure equalization may be effected between the spring suspension cylinder and the suspension reservoir and in this way uncontrolled movement of the axle when the suspension system is activated may be prevented.

[0001] The invention relates to a spring suspension system, in particular for a machine such as a tractor or the like, with a spring suspension cylinder to which varying load pressures may be applied, a suspension cylinder whose piston and rod side may each be connected as required to a spring suspension reservoir by way of a locking device which locks the spring suspension system, and with a load equalization device which effects load equalization to the currently prevailing load pressure before the spring suspension is activated.

[0002] In certain spring suspension systems, for example for machines such as tractors or the like, it may be advisable to stop such machines, for example at a speed below an assignable speed of the machine. This is accomplished by locking the hydropneumatic suspension when the vehicle is moving at low speeds or is stationary. Operations such as hoisting and loading and unloading loads or activation of harvesting or other implements may accordingly proceed without disruptive vehicle spring suspension travel.

[0003] Since the load situation is unknown after such operations as the vehicle continues in movement or starts movement, in the known spring suspension systems movement of the vehicle or operating machine is not controlled when the suspension is unlocked; this is in principle an unacceptable situation.

[0004] Hence the object of the invention is to develop, starting from this state of the art, a spring suspension system which eliminates the disadvantage described in the foregoing. The desired objective is achieved in full by a spring suspension system having the features specified in claim 1.

[0005] Provision of the spring suspension system with an equalization device makes it possible to effect equalization of the pressure of the system to the currently prevailing load pressure before the spring suspension is reactivated. Hence, with the spring suspension system claimed for the invention pressure equalization between the suspension cylinder and the associated suspension storage reservoir is effected and so uncontrolled movement of the shaft is prevented when the suspension system is engaged, independently of the change in load.

[0006] In a preferred embodiment of the spring suspension system claimed for the invention a sensor device monitors the current operating position of the actuating piston in the suspension cylinder and even slight movement in the area of the suspension cylinder triggers pressure equalization independently of change in load.

[0007] Other advantageous embodiments of the spring suspension system claimed for the invention are specified in the subsidiary claims.

[0008] The spring suspension system claimed for the invention is discussed in detail on the basis of an embodiment, with reference to the drawings, in which

[0009] FIGS. 1 to 4 illustrate in diagrammatic form a wiring diagram for the spring suspension system claimed for the invention in various states of operation.

[0010] The spring suspension in FIG. 1 is shown in its locked state, that is, the suspension feature proper of the suspension system is disabled.

[0011] The suspension system in question has a suspension cylinder 10 to which varying load pressures m may be applied; the piston side 12 and piston rod side 14 may each be connected to a spring suspension reservoir 16 or 18 by way of a locking device designated as a whole as 20, the locking device 20 locking the spring suspension in the switched state illustrated. The spring suspension 10 is connected by way of its housing to a vehicle body not shown in detail and is linked at the free end of the piston rod 24 connected to the piston 22 to a vehicle wheel 26, a plurality of vehicle wheels together with associated spring suspension cylinders (not shown) ensuring operability of the machine such as a tractor or the like. The spring suspension system also has an equalization device designated as whole as 28 which engages or disengages the cylinder with the aid of the supply device.

[0012] As FIG. 1 also shows, the two suspension reservoirs 16, 18, which are in the form of conventional hydraulic reservoirs such as membrane reservoirs or the like and the locking device 20 are connected to a supply device designated as a whole as 30, which is to be regarded as part of the equalization device 28 and which ensures connection at option to a pressure supply source P and/or to a tank connection T by way of a switching device designated as a whole as 32. In addition, the two suspension reservoirs 16, 18 are each separable from the supply device 30 by way of a return valve 34, 36 each of which is held in a closed position by a spring under load and move into their open positions in the direction of the relevant spring suspension reservoir 16 or 18.

[0013] A releasable return valve 43 is mounted in a branch line 38 of the line 40 leading to the closing device 20 of the suspension cylinder 10. Opening control line 41 of releasable return valve 43 is connected to the control line LS of the supply device 30 and a line 45 between the return valve 36 and the 3/2-way switching valve 50. The fluid control connection for this purpose is made at connecting point 47. A response to the load sensing system may be made over the connection for this purpose so that the hydropump P supplying the system may assume system pressure. The releasable return valve 43 itself is connected between lines 38 and 40. In addition to the line 40 on the piston side, an additional line 42 is connected to suspension reservoir 18 and associated return valve 36 on the rod side 14 of the suspension cylinder 10.

[0014] The locking device 20 in question has both for the piston side 12 and for the rod side 14 of the suspension cylinder a 2/2-way pilot valve 44, 46 which, while in its inactive basic position shown in FIG. 1, blocks the fluid conducting path from the suspension cylinder 10 toward the suspension reservoir 16, 18 and under spring loading opens the path in the other direction. Hence in the locked position shown in FIG. 1 the suspension cylinder 1, with its piston side 12 and its rod side 14, is separated from the associated suspension reservoirs 16 and 18, and accordingly the suspension system is locked so that spring deflection or rebound of the vehicle (not shown) is not possible and change in load m cannot result in undesirable spring deflection or rebound of the total system.

[0015] The equalization device 28 in question has, both for the piston side 12 and for the rod side 14 of the suspension cylinder 10, within the supply device 30, a 3/2-way pilot valve 48 or 50 which in their unactuated initial position are connected to each other by way of a connecting line 52 to the tank connection T and on their inlet side are additionally joined together by another connecting line 54 so as to conduct fluid. In addition, the suspension cylinder 10 has a sensor device not shown in detail by means of which it is possible to monitor the position of the piston rod 24 and/or of the piston 22, the sensor device (not shown in detail) forwarding its signals to an electronic interpretation unit, which in turn activates the pilot valves 44, 46, 48, and 50 for an actuation process. Activation for the purpose of effecting pressure equalization prior to activation of the spring suspension will now be explained in what follows.

[0016] First of all reference is made once again to the state of the system as illustrated FIG. 1. In the situation shown the spring suspension is locked and the suspension cylinder 10 is in level position. Deflection or rebound of the piston 22 with piston rod 24 is consequently not possible, since discharge of fluid on the piston side 10 or the rod side 14 is prevented by the pilot valves 44, 46 in their closed position. In the locked position as shown, locking by way of pilot valves 44, 46 is achieved in that a return valve integrated into them can open in the direction of the spring suspension cylinder 10, but is kept closed in the opposite direction, that is, in the direction of the suspension reservoir 16, 18. Increased pressure on the suspension reservoir 16, 18 side would thus result in opening of the pilot valves even in their locked position in the direction of the suspension cylinder 10. If the load or load pressure m remains unchanged in the switching position shown in FIG. 1, the pressure on the piston side 12 corresponds to the fluid pressure of the reservoir 16 and the fluid pressure on the rod side 14 corresponds to the fluid pressure of the suspension reservoir 18, the pressure on the rod side corresponding to the pressure of the system. In order to prevent, in this situation, uncontrolled movement of the vehicle wheel 26 and accordingly of the movable parts of the suspension cylinder 10 when the suspension is activated, pressure equalization must first be carried out between the suspension cylinder 10 and the suspension reservoirs 16, 18.

[0017] In order to achieve this pressure equalization, in a first step, as illustrated in FIG. 2, the 3/2-way valve 50 is activated and the other line 42 connected to the hydraulic pump P. Since the pilot valve 48 remains in its unactuated position as illustrated, the pump pressure is blocked by the pilot valve 48 in the other connecting line 54 in the direction of the first line 40. If the pressure on the piston side 12 corresponds to the load pressure required, movement begins immediately on the suspension cylinder 10 and the piston 22 with piston rod 24 begins to travel in the direction of the piston side 12 of the suspension cylinder 10. The pressure in the suspension reservoir 16 may be even lower than the pressure on the piston side 12 of the suspension cylinder 10. In particular, the excess amount of fluid in movement for the purpose as indicated by the arrow from the piston side 12 is expelled in the direction of the side branch.

[0018] If the pressure on the piston side 12 is above the required load pressure m, first fluid, especially hydraulic fluid, is drained from the suspension reservoir 16 by way of the 2/2-way pilot valve 44 as indicated by the arrow in FIG. 3 to the tank T, until the load pressure m has been reached. Once the load pressure has been reached, movement of the suspension cylinder 10 begins and the cylinder travels in the direction of the arrow. When the suspension cylinder starts to travel, hydraulic fluid is drawn from the associated reservoir 18 on the ring or rod side 14 of the suspension cylinder 10 and so pressure equalization is established between cylinder pressure on the rod side 14 and reservoir pressure for the suspension reservoir 18 at system pressure. If the control system (sensor device, interpretation electronics) detects movement at the system suspension cylinder 10, the first step toward pressure equalization has been completed. The pressure on the rod side 14 of the suspension cylinder 10 then corresponds to the storage pressure of the associated suspension cylinder 18 and both pressure values correspond to the system pressure. Lastly, the valve 46 is actuated and then assumes a switch position as shown in FIG. 4.

[0019] The next, second, step to pressure equalization now consists in switching of both the 3/2-way pilot valve 50 and the 3/2 way pilot valve 48 to the position allowing supply of line 40 or 42. In the switching state shown in FIG. 4 and achieved for this purpose, the piston 22 with piston rod 24 now emerges from the suspension cylinder 10 in the direction of the arrow. If the reservoir pressure of the suspension reservoir 16 now corresponds to the required load pressure m, movement at the suspension cylinder 10 begins immediately and the suspension cylinder 10 is extended. But if the reservoir pressure at the suspension reservoir 16 is initially lower than the required load pressure, in a first step the suspension reservoir 16 is charged to load pressure by way of the associated return valve 34 in the line 40. If the load pressure has been reached, movement begins at the suspension cylinder 10 and the piston 22 with piston rod 24 is extended. Since the system of piston 22 and piston rod 24 rests on the unsprung mass which customarily may be in contact with the ground, extension of the system of piston 12 and piston rod 24 is equivalent to lifting of the sprung mass. In the case of the extension movement of the suspension cylinder 10 referred to, the pressure on the piston side 12 equals the pressure in the suspension reservoir 16 and this in turn equals the load pressure m. The control unit referred to above, consisting essentially of the sensor device not shown in detail and the interpretation electronics, detects the movement at the suspension cylinder 10 and the pressure equalization is then considered to be complete. Valves 48 and 50 in turn are shifted to their blocked position as shown in FIG. 1 and after engagement of the upper 2/2-way pilot valve 44 as seen in the viewing direction, the spring suspension is open, that is, both the piston side 12 and the rod side 14 are connected to the suspension reservoirs 16 and 18 associated with them in a fluid conducting state for a spring suspension process.

[0020] Equalization of pressure between suspension cylinder 10 and the associated reservoirs 16, 18 is effected by the circuitry shown and the switching process described, with slight movement at the suspension cylinder in one direction or the direction opposite it, independently of possible change load m, so that uncontrolled movement is prevented when the suspension is engaged.

[0021] In an embodiment of the invention not shown, the sprung masses maybe replaced by unsprung masses, the circuitry of the suspension system being more or less retained, that is, the hydraulic components described remain connected as illustrated both to the piston and to the rod cavity of the suspension cylinder 10, the advantages referred to being retained as a result of the exchange made for the purpose. In another embodiment (not shown) it is also possible to detect the differential pressure present upstream and downstream from the pilot valve 44 with conventional measurement devices. In the event that no differential pressure (permissible tolerance: minimum differential pressure) exists, the second step for pressure equalization as described in the foregoing may be dispensed with and accordingly the spring suspension may be released even more quickly.

[0022] Only the most important components of the spring suspension system claimed for the invention are shown in the illustrations and corresponding throttles and return valves for damping of the system and the path-measuring system itself for measurement of movement of the state of the system at suspension cylinder 10 have been omitted from the circuit diagram. 

1. A spring suspension system, for a machine such as a tractor or the like, with a suspension cylinder (10) to which different load pressures (m) may be applied, the piston (12) and rod (14) sides of which may each be connected to a suspension reservoir (16, 18) by way of a locking device (20) which blocks the spring suspension, and with an equalization device (28) which effects equalization of the pressure of the system to currently prevailing load pressure (m).
 2. A spring suspension system as specified in claim 1, wherein the suspension reservoirs (16, 18) and the locking device (20) are connected to a supply device (30) as part of the equalization device (28), which provides connection optionally to a pressure supply source (P) and/or to a tank connection (T) by means of a switching device (32).
 3. A spring suspension system as specified in claim 2, wherein the suspension reservoirs (16, 18) may be separated from the supply device (30) each by way of a return valve (34, 36) which is held spring loaded in its closed position and which assumes its opened position in the direction of the pertinent suspension reservoir (16, 18).
 4. A spring suspension system as specified in claim 3, wherein an overload monitoring device (LS) which activates the pressure supply source (P), in particular in the form of a hydropump, is connected to a branch (38) to the line (40) with the locking device (26) and with which may be associated the suspension reservoir (16) with return valve (43) for the piston side (12) of the suspension cylinder (10), so that such pressure supply source (P) delivers the system pressure required.
 5. A spring suspension system as specified in claim 4, wherein the suspension reservoir (16) is connected to the line (40) by the return valve (34).
 6. A spring suspension system as specified in one of claims 1 to 5, wherein the locking device (20) has for both the piston side (12) and for the rod side (14) of the suspension cylinder (18) a 2/2-way pilot valve (44, 46) which when in its unactuated base position blocks the fluid conducting path to the associated suspension reservoir (16) and frees such path in the opposite direction.
 7. A spring suspension system as specified in one of claims 1 to 6, wherein the equalization device (28) has for both the piston side (12) and for the rod side (14) of the suspension cylinder (10), inside the supply device (30), 3/2-way pilot valves (48, 50) which when in their unactuated base position are connected to the tank connection (T) and on their inlet side are connected to each other so as to conduct fluid.
 8. A spring suspension system as specified in claim 7, wherein an opening control line (41) for a releasable return valve (43) is connected to a line (45) between the return valve (36) and the 3/2-way valve (50).
 9. A spring suspension system as specified in claim 7 or 8, wherein the suspension cylinder (10), in particular the position of the piston rod (24), is monitored by a sensor device which transmits to a data interpretation unit its signals, which activate the pilot valves (44, 46, 48, 50) for a switching process. 